Do we mean the top five we actually grow? or the top five we would like to grow if we #A could lay our hands on a corm #B were able to grow them?
The last one shown by Janis would be one of them.
Of those I have grown my top five would be:
Speciosus
Speciosus albus,
'Ladykiller'
'Princess Beatrix'
Banaticus (which I find difficult)
This is the list of the uninitiated.

Most crocus are very beautiful so the choice is difficult.
German Burg Swedish borg means castle (never city) just as Joakim writes. However, since medieval towns often started around castles many towns all over Europe From Burgos to Borgå
got burg in their name. Göteborg probably got its name because it was well fortified. The word also has a general flavour of safety in Swedish. Derivates of the word are used in guarantees of loans.
I assume that the Romans introduced the word castellum for the original meaning of fortress and thus, in the English language, Burgh, Borough came to mean town only.
Göte